Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$128.89	8.584%	$139.9539	$139.95	$139.95	$140.00
Purchase #2	$28.55	4.577%	$29.8567	$29.86	$29.85	$29.90
Purchase #3	$28.79	7.859%	$31.0526	$31.05	$31.05	$31.10
Purchase #4	$105.68	3.231%	$109.0945	$109.09	$109.10	$109.10
Purchase #5	$105.57	9.531%	$115.6319	$115.63	$115.65	$115.60
Purchase #6	$93.63	12.824%	$105.6371	$105.64	$105.65	$105.60
Purchase #7	$105.47	10.524%	$116.5697	$116.57	$116.55	$116.60
7 purchase totals =	$596.58		$647.7964	$647.79	$647.80	$647.90